Yes indeed but having an opinion that 'a' is useless may well be normal but saying it does not make it legitimate or reasonable does it? That particular example is neither 'advertising' nor 'selling as better or supreme' but it is blatantly rude and offensive wouldn't you say?
In my opinion it cannot actually be true either for what anyone says is useless is obviously useful to those who do it. When I call someones art useless I may not be 'selling' but what am I doing?
Looking at what we say and knowing when it's negative is the starting point.
By the way cheesy is what I would call that guy doing the gangnam style rapping and dancing.
If someone expresses an opinion in a manner that is aggressive, rude, or offensive, I agree that there is nothing constructive about it and they should keep it to themselves or be ignored.
It is possible to express an opinion, even a negative one, in a respectful manner. I think it takes a certain amount of discipline, however, to do this. It also takes discipline to not take a criticism or a negative opinion personally.
Free (respectful) speech!